Contagious Chemistry
by BeeBops3
Summary: I had finally returned 'home' after five years, to find I was still cast as the girl who was overshadowed by my brother, but at least I was back. But what do you do when tragedy strikes? You can plan for every eventuality but no one really knows what they will do in any situation until they are really there. And was I really ready to have to make these decisions? AU HP OC.
1. Chapter 1

**I would love if you guys could review and let me know if you would like to see more of where this is going!**

 **Disclaimer:** I do not own any of Harry Potter.

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It was such a bizarre sensation, to be standing somewhere that I had been remembering in my dreams for the last five years. Nothing had changed really, not that I had expected it too, except for the people, some I recognized only older and a hell of a lot of new ones. I guess, technically to all of these people though, I was new, five years is a long time to be away and to still consider yourself part of the woodwork. I was snapped out of my subconscious though when a hand was placed gently on my shoulder and I turned to see a warm smiling face, that hadn't changed a single bit.

"Caillen, it is so good to have you back!" came the delighted tone of the illustrious Albus Dumbledore, renowned headmaster of Hogwarts. I felt the smile spread across my face and the overwhelming sensation that I was finally back where I belonged. "I'm so glad to be home!" I exclaimed a little too high pitched for my own liking, drawing the attention of some of the students who were passing by. He laughed and began walking in the direction of his office and I naturally followed, taking in all the corridors, tapestries, statues and ghosts along the way, thanking my almost eidetic memory for never letting me forget this place.

When we entered his office, Fawkes was perched on his post and I swear he was happy to see me, as he ruffled his feathers and gave a nod in my direction. Before I had even taken a seat though, his office door burst open and in fell a pile of bodies all trying to be the first one through the door. I stifled a laugh as I studied the faces all picking themselves up from the ground, and like a rolodex my brain started going through the many people I had met in my life and attaching names to these faces. For the most part it was blatantly obvious, with their shocks of bright red hair flopping over their faces we had; Fred, George and Ron Weasley. And once they had straightened up I could see we also had Seamus Finnigan, Dean Thomas and the boy wonder himself Harry Potter. "Boys, I told you not to go barging in there!" the exasperated voice of Professor McGonagall came flowing in after them, before she too appeared in the doorway to the office.

She was about to speak again when she noticed all of them were silent and still, as though they had just been petrified, and that's when she looked over to where they were all staring, and of course seen me. "Caillen my dear?!" as the words left her mouth she moved quicker than even I could remember she could and grabbed me in an embrace that was extremely unpredicted. "I didn't know we would be seeing you again…" she began before shooting one of her classic looks across to Dumbledore, "Albus! You knew and you never said?!" she snapped, but shook her head and smiled none the less. Before I even had a chance to speak I realized we still had an audience and things were quickly becoming awkward, so I just stepped past Professor McGonagall to face the gate crashers of my return meeting.

"Hello boys, what can I do for you?" I gave a cheeky smirk, attending school in America for 5 years I had picked up a lot of their mannerisms but never once did my broad Scottish accent fade. Seamus didn't look like he even knew how to speak anymore, Dean had already started backing out the room, Ron and Harry just looked from me back to each other over and over again which made me laugh and then the Weasley twins, you could always count on them to break the tension. Fred stepped forward, quickly followed by George, "Sorry to intrude on, whatever this…is," he waved his arms around the room, "But we heard Wood's was back and we were all just dying to see him…but instead we seem to have found you…" he trailed off only for George to finish the sentence, "Not that any of us are complaining about that though!" they both winked at the same time and now I couldn't even stifle my laugh. Professor McGonagall was about to interject when I could hear "Minervra…" being whispered in a tone that suggested just letting this play out.

"That's the trouble with rumours, they spread so quickly." I quipped, all eyes still firmly rooted on me. Now had I been back in Ilvermory, I would have probably just left the room at that point. I had built quite the reputation for myself based on my sarcasm and unwitting ability of being a bit of a bitch, but that's what happens when you get sent to a school you don't want to go to. I had swore to my parents if they allowed me to go back to Hogwarts now that I was 16, I would actually behave this time, and not actively try to turn people against me, so no time like the present to start. I smiled sweetly, not something I did very often, which evoked a raised eyebrow from Professor McGonagall that I chose to ignore and stuck my hand out. "You did hear correctly though that Wood was returning, you just all assumed it would be my, _oh so amazing, talented, star quidditch playing_ , older brother. Sorry to disappoint." I drawled out – I said I would try to be nice, I didn't say it would come easy – imitating every girl and most guys I had ever met when it came to talking about Oliver.

The boys all looked stunned, Seamus's face hadn't really changed to be honest, but the rest were now standing with the usual confused expression, I was used to seeing at the announcement of my existence from my brothers big ass shadow. "Oliver has a sister" George said to Fred, who nodded but with an look that read, I had no fucking idea either. I could see the questions formulating in their minds, and thankfully so could the professors, who ushered them out at this point before anything more could be said. McGonagall gave me a final squeeze, then continued shooing them out the room and locking the office door behind her. Maybe I should have just stayed in America…

As quickly as that thought entered my head, was as quick as it left again, I couldn't really deny how happy I was to be back here after all this time, even if it did mean I was undoubtedly back in my brothers shadow. "It's always the same you know…" I sighed, throwing myself down onto one of the large plush armchairs that sat in the corner of the office. "But you my dear, are a remarkable witch in your own right, and we couldn't be happier to have you finish out your schooling here." Dumbledore spoke softly, knowing a little ego boost always helped after a comparison to my champion of a brother. "Thank you Professor, you're too kind" I joked, pretending to be embarrassed. "So… please tell me I don't need to be sorted… again?" I questioned, as my eyes caught to sorting hat perched on the shelf to my left.

I was sorted as every young witch and wizard is, on my first day at Hogwarts and was placed into Ravenclaw, which was no surprise to me, but to much distain of my family who expected me to continue on the family path. But I mean an eidetic memory only really works for Ravenclaw. But then when I was transferred to Ilvermory for my second year, due to my father working over there, they made me go through their entire sorting ceremony along with all the first years, which set me off on a bad note with the school from the outset, and I landed in Wampus and not the Horned Serpent like I had wanted. So now that I was back, I was hoping I could just slip back to Ravenclaw as the sorting hat had first predicted and get on with my school year from there. But I could see the look on Dumbledore's face and knew I wasn't about to like the answer. "If you had been sorted into the Horned Serpent then I would have no issue placing you back into Ravenclaw, but because you weren't I feel the most responsible action is to have the hat decide…" he trailed off as I sat like a petulant child in a huff. "But we can just do it here, instead of at the ceremony, so you have time to settle before supper!" I looked up as he said this, and he dropped the hat straight onto my head, and I couldn't believe I didn't see that coming. I basically ignored the hat; you get used to it by the third attempt and jumped as he yelled "GRYFFINDOR!" I don't think it realized there was no audience to appeal too. And my heart sank knowing how happy my family would be that I was finally fore filling the family honour and would graduate a Gryffindor. I gave a pathetic smile to Professor Dumbledore as I unlocked the office door and headed off no doubt in the exact same route as all the boys who left not too long before me. Yet again I wondered if I should have just stayed in America…


	2. Chapter 2

Thank you for those of you who are returning here for chapter 2, I have so many ideas firing through my head for this story and would love to hear for you all what your thoughts are on it too!

 **Disclaimer: I do not own any rights to the characters or property within Harry Potter.**

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Remaining the petulant child that I am, I glumly walked toward Gryffindor tower and realised while on my way there, that I had absolutely no idea what the password was to enter. Now, had I not been the stubborn bitch that I am, I would have just turned back to ask for it. But instead I did what any inflexible adolescent would, and I kept on walking, my soft dark brown curls bouncing gently round my face. I sighed as I turned the corner, not paying attention to where I was going, images of the familiar faces I seen not long before, jovially getting ready into their robes for the welcome feast. As I continued down a corridor that I could evidently see came to a dead end, I had the oddest feeling, like I was being watched. I stopped walking, and noticed that whoever was behind me did the same.

I was about to turn round to see who was there, but ended up frozen to the spot as they spoke; "Well aren't you a sight for sore eyes…Wood…" as these words reached my ears, memories from my childhood came flooding back, and I spun round to face the devilish smirk I knew would be standing there. I got a strange feeling in the pit of my stomach as my dark green eyes met with his steely blue ones, and I found myself completely lost for words. Still trying to process what was happening in my head, he spoke again as he strode towards me, "Don't tell me, that brain of yours has forgotten me?" he toyed, looking deeper into my eyes, and now standing toe to toe with me. The feeling in my stomach grew stronger as I looked up at him, not far from my face, and finally found my voice again, "How could I ever forget that hair?!" I laughed, gently shoving him, and unconsciously taking a step back creating some space between us.

If he noticed this, he never mentioned it as he too laughed and a genuine smile spread across his face, just like the one I recalled from when we were young. Neither of us had the chance to say anything more, as I could sense people approaching from behind me and seen his face turn cold, the smile quickly dissipating, as a female voice spoke carrying an air of venom with it; "What have I told you about picking up strays Drakey?" she all but purred, as she passed around me, draping herself around his neck, while the two goons who had been approaching with her, parked themselves uncomfortably close on either side of me. I once again took a step backwards, glaring at the oafs towering over me, the situation seeming somewhat familiar to an altercation I had just last year, with the old Queen Bee of Thunderbird house back at Ilvermorny.

I glanced across at Draco and his shawl, who he swiftly shrugged off him when he seen me looking over, gaining a disgruntled moan from her. "Don't want to overstay my welcome, _Drakey…_ ´I mocked, whilst turning my back and rolling my eyes, hearing the sound of her quickly reaching for her wand and the screech that she emanated as it was smacked out of her hand. I knew better than to turn around, as I said, I had been in this sort of situation before, so I just sped up my pace until I was once again standing in front of the Fat Lady painting. I hadn't even noticed the solitary tear that had been tracking its way down my tanned cheek, as I continued to pace in front of the painting, I must have been starting to get on her nerves as she was copying my movements now, agitatedly shaking her head whenever I looked over to her. I had just looked away again to rub my eye when I felt the damp trail down my face but I didn't have time to ponder it as I heard the painting swing open behind me.

Without hesitation I lunged towards it, crashing into the people who were making their exit from the common room, landing face first on the stone floor beneath me. "Woah! Slow down!" the first voice laughed, followed very swiftly by another, which was far less friendly "You cannot break into other common rooms you know." I dusted myself off, remembering the promise I had made to my parents, and swallowed the hostile response I wanted to spit back. "I'm sooo sorry…" I began, cringing on the inside at the sound of my own voice, and before I continued I realized the first person that spoke was Ron. So I directed the rest of my statement towards him, ignoring the visibly agitated girl that I could now place as Hermione Granger, the only girl to ever come remotely close to me academically, figuring I would just sort things out with her later.

"I really am a Gryffindor... See?!" I proclaimed whilst easily passing the charmed barrier and looking back to see the youngest Weasley son smiling. I smiled back and continued. "I just didn't think to get the password and have been waiting out here foreeeeeever! But if you will please excuse me, I am already going to be late for the feast!" and with that I jumped back into action, dashing up the stairs and leaving Ron to answer the tirade of questions Hermione started to fire at him. I reached the common room within seconds, taken a back slightly at what I seen before me, I don't know why I just hadn't imagined it to look so warm and inviting. There were lots of people, all clearly ready to make their way down to the Great Hall and now all looking at what clearly appeared to them as some sort of intruder.

I scanned the crowed that was quickly forming around me, looking for familiar faces that may also remember be and that's when I heard a shriek and then a set of arms engulf me. "Caillen? Is that really you?" The warm tones of Angelina filled my ears and I peeled back from her embrace to look at her. "Jelly!" I was so happy to see her, not least because once she had hugged me, no one seemed that bothered by my presence anymore. "It has been far too long! How are you? How was Ilvermorny?" The questions just kept coming and I couldn't keep up answering them. I had met Angelina on her first Christmas break from Hogwarts, her father and mine had become close through work and Oliver couldn't wait for her to join the Gryffindor quidditch team and until I left for Ilvermorny she spent a lot of time at our home during breaks, and afterwards kept in touch with occasional owls carrying a years' worth of updates in one letter. Thankfully being late was on my side, as she had to leave, but before she left I realized something important, "Jelly… where will I be sleeping?" I asked puzzled, knowing that all the spare beds would be in the 1st year dormitories and praying that I was not going to have to share with a bunch of 11 year old girls.

She paused for a second, as though also processing the same thought trail that I had just ran through and then laughed, "I know what you're thinking… don't worry no friend of mine is getting stuck in a room with the children!" I hadn't noticed how tense I was at that thought until I felt my shoulders physically relax and hear Fred Weasley once again break the tension by yelling, "She can definitely sleep in my room!" This evoked whistles and cheers from others that were in the room, and I just pictured Oliver's reaction had he been here, which made me chuckle. Angelina thought I was laughing at the remark though and sent me a stern look, which to this day I still don't understand considering she was dating the other one! It was in that moment that Ron suddenly reappeared and I first noticed his Prefect pin and also recalled seeing the same thing on Draco's robe as well. Ron explained he had been sent back by Professor McGonagall to speak with me and chase everyone else down to the Great Hall or points would already be deducted from Gryffindor. We stepped aside and I watched them all clear out quickly, not wanting to be the cause of a loss of points on the first day of term.

"McGonagall wanted me to firstly tell you that the password is Dilligrout, and that she should have known you would be too stubborn to go back and ask for it.." he paused as though waiting to see if I was insulted, which of course I was but I wasn't going to let onto that as I wanted to know what else he had to say, so I just nodded politely and raised my eyebrows signaling for him to continue, which he did. "She also said you would be wondering if you had to sleep in with the first years and that she did consider this as a retribution for your stubbornness, but decided that may fall into the category of cruel and unusual punishment…" he shifted awkwardly, not wanting to meet my eye, but I wasn't going to shoot the messenger. "Oh for Merlin's sake Ron, where did she say I was going to sleep then?" I snapped slightly, I said I wasn't going to shoot the messenger and by that I meant with a spell, not my attitude. He didn't even flinch though, breathed what seemed to be a sigh of relief that that was my reaction and started walking away from the staircase to the dormitories, "She said that might annoy you, so sorry about that," he laughed now as I followed him to the other side of the common room, intensely intrigued at where he was leading me. "As there are no beds in with the other 6th year girls, she has opted that you take this room…" and at that he led me up a staircase I hadn't even noticed, but was astonished to see that we could both walk up it, without one of us causing it to turn into a slide. I was busy thinking about that when we reached the top and with his wand out and "Alohomora" I found myself standing in a room, all to my very self.


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